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Booming notes on Yamaha RBX765

Discussion in 'Hardware, Setup & Repair [BG]' started by Mottlefeeder, Apr 2, 2004.

  1. I've searched set-up and luthier, and not found a relevant thread, so please redirect me if I have missed something.

    My RBX765 is strung with lightweight Rotosound 66 stainless steel 125/100/80/60/40g strings, tuned BEADG. The problem that I have is a 'cheap car stereo' boom about the F on the B string or the C on the E string. It is less obvious with new strings, and gets worst from there.

    It is not a fret buzz, or a room/speaker resonance. It does not appear to be an electronics problem, because the same notes on other strings sound much better, and it does not appear to be a pick-up problem, because the better sounding F is on the E string.

    Is this a dead-spot type problem with this bass, or a string incompatibility problem, or some other resonance that you can tell me how to track down?
  2. Mine does too. I've always assumed it was normal on the E and B strings, as you move farther down (or is that up?) the fretboard, it starts to get boomy. Part of it is the fact that my amp gets a bit excited at certain frequencies in certain rooms. I played outside once and the problem wasn't as noticable...
  3. pkr2


    Apr 28, 2000
    coastal N.C.
    Purely a guess, but I'd check the pup height very critically.

    Harrell S.
  4. Your condition is called a "woof" tone. It's the resonant frequency of a room or cabinet or both. Like you've experienced, get'em sync'ed up and you could level Pompeii!

    That's not what the Mott has got. [unintentional rhyme :eek: ] It sounds like a resonance problem but I'm just guessing like Harrell. You might be able to tell if you use a small "C" clamp (metal or plastic) and attach it to various spots on the neck and body to see if you can get the booming notes to move or decrease or just change in general. Be careful and pad the ends of the clamp. This isn't a cure, just a test method. If you CAN get it to change, you are probably looking at some sort of internal resonance thing that likely won't be able to be cured. It could come from a strange interaction between the way 2 dissimilar pieces of wood are attached or the way the grain grew. These instruments are built from natural materials that can sometimes have a mind of their own.
  5. I am reasonably happy working with intonation, adjusting the truss rod after changing the string gauge etc. but I have never done anything with the pickups.

    I have noticed that the bad sound is more noticable on the neck PU than the bridge PU, so it sounds as if I need to look into that.

    Would you suggest moving the PU away from the strings or towards them?
    Would you expect a dramatic difference for a small movement, or a gradual change?
  6. pkr2


    Apr 28, 2000
    coastal N.C.
    I would lower the pup ht. at least 1/16" or so and check the "wolf tone" (for lack of a better description) and see if there's an improvement. It's not a very critical measurement,normally.

    Harrell S
  7. I made a start last night, and found something that I did not expect - I can still hear a resonance on the E string C with the bass unplugged, so it would appear to be a mechanical problem not an electrical one.

    I've damped the springs on the bridge, and checked for flapping wires in the electronics compartment, but no joy so far.
    My next action looks like taking off all the controls and electronics, and removing them from the bass (but still keeping them connected to the pups). The alternative would be to check what is happening under the pups. I'm guessing that there should be a spring under each to push up against the pup positioning screws.
    I'll post again when I find the problem area.
  8. pkr2


    Apr 28, 2000
    coastal N.C.
    The magnets in the pups can affect the strings motion via magnetic coupling if the string is too close to the magnet. Doesn't matter if the bass is unplugged or not.

    Yes, there should be something to hold the PUP up. Either springs or sometimes a pad of foam rubber is used under the pup to hold it up.

    You should be able to just push the pup down into the cavity to determine if its a height prob. If the prob clears up while holding the pup down, then turn the screws for a permanent adjustment.

    What kind of bass is it?
  9. The Yamaha RBX series is the more modern looking one, i.e. not the BBN shape that Nathan East plays. The 765 is the five string, cast bridge, humbucking soapbar pups, 4-pot (vol/ Pup-pan/ treble/ bass) active version.

    I tried to push the pups down last night, but with thumb pressure in a normal playing position, I could hardly move them at all, perhaps a sixteenth of an inch at one end or the other, but no movement at all pushing in the middle of the pup. The screws also seemed very tight compared with comparable sized bridge adjustment screws - interesting.
  10. I couldn't push the pup down, fret the string and pluck it at the same time, so I used the adjustment screws. dropping both pups by about 2-3 mm taking them both more than 5 mm from the strings, and it makes no difference to the resonance.

    I don't see much alternative to taking bits off until I find the culprit, or run out of bits. - Anyone remember the scene at the end of 'The Converstation' where Gene Hackman is taking his apartment apart to find a bugging device?
  11. pkr2


    Apr 28, 2000
    coastal N.C.
    Good luck. Let us know the outcome.

    Harrell S
  12. I've loosened the strings, removed both pups, removed the battery box, the control pots and the electronics, wrapped each part in bubble wrap, and tuned up again.

    I still have the resonance at C, but I now have it on the next two frets up and down as well. I'm beginning to wonder if the bass has some small resonance at this frequency, and the Rotosound string has a resonance at the same frequency as it starts to wear out - separately you cannot hear them, but together you can.

    I have e-mailed Rotosound about the resonance as a symptom of wear-out, but they did not answer that bit of my question. They did say that the B and E strings were more prone to winding problems because they used three layers of wire.

    I think its time I tried a different tpe of string.
  13. I took the S/S light gauge Rotosounds off, and put on Nickel standard gauge Ernie Ball Slinkys.

    I have adjusted the truss rod for the increased tension, but still needed to drop the bridge and re-do the intonation.

    The resonance has gone! I am not sure if the change in tension did the trick, or the change in string construction - the EBs appear to only have two windings on the E string, so maybe their mix of harmonics is different.

    All I need to do now is find a cheaper source for Ernie Balls, or a cheaper equivalent.

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